Abstract
ABSTRACTFruit flies (Drosophila melanogaster) eclose from their pupae mainly around dawn. The timing of eclosion is thought to confer adaptive benefits to the organisms and thus shows remarkable accuracy. However, it is not clear what factors are involved in the evolution of such accuracy in natural populations. In this study, we examined the relative contributions of gating of eclosion by the circadian clock versus clock-independent developmental rates and light-induced responses in the eclosion phenotype exhibited by fly populations that have evolved greater accuracy in eclosion rhythms compared to controls. We compared variation in timing of transitions between early developmental stages (pupariation and pigmentation), overall development time under constant light conditions – where circadian clocks are dysfunctional – and eclosion profiles when developmental rate was manipulated using different larval densities in selected and control stocks. Our results showed that stocks that have evolved greater accuracy of eclosion rhythms due to artificial selection do not show reduced individual variation in pupariation and pigmentation time compared to controls, though they do exhibit lower variation in eclosion time. Selected stocks also did not show lower variation in eclosion time under constant light conditions in contrast to the greater accuracy seen under light-dark cycles. Moreover, manipulations of developmental rate by varying larval density and inducing eclosion by changing onset of light phase did not alter the eclosion profile of selected stocks as much as it did controls, since selected stocks largely restricted eclosion to the daytime. These results suggest that fly populations selected for greater accuracy have evolved accurate eclosion rhythms primarily by strengthening circadian gating of eclosion rather than due to fine-tuning of clock-independent developmental processes.This article has an associated First Person interview with the first author of the paper.
Highlights
Eclosion rhythms are thought to have evolved as a consequence of adaptive benefits conferred to insects by emerging in the early part of the day (Pittendrigh, 1954; Cloudsley-Thompson, 1960; Tanaka and Watari, 2009)
We examined the contributions of such non-clock processes involved in the regulation of eclosion time in the evolution of greater accuracy in fruit fly populations selected for narrow gate of eclosion
Pupariation, pigmentation and eclosion of selected and control stocks under LD 12:12 We assayed the timing of transitions between developmental stages such as pupariation and wing pigmentation that are not known to be under clock control in Drosophila to determine whether the selected stocks have evolved differences in developmental rate (Fig. 1A–F)
Summary
Eclosion rhythms are thought to have evolved as a consequence of adaptive benefits conferred to insects by emerging in the early part of the day (Pittendrigh, 1954; Cloudsley-Thompson, 1960; Tanaka and Watari, 2009). The daily timing of eclosion (or eclosion phase) in Drosophila melanogaster populations is noted to be highly accurate (Kannan et al, 2012a) though it is not clear how such accuracy evolves and what factors may contribute to accuracy of the eclosion rhythm. Rhythmic behaviours such as eclosion and locomotor activity in D. melanogaster are known to be under the control of the circadian clock. Theoretical studies on accuracy and internal periodicity and clock-resetting have suggested a close relationship between the accuracy of phase and these clock properties (Pittendrigh and Daan, 1976a; Beersma et al, 1999). There are no reports of comprehensive studies examining the relative roles of clockdependent and clock-independent factors in the evolution of accurate circadian rhythms
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